Expandable fixation elements for subcutaneous electrodes

ABSTRACT

Subcutaneous systems and leads may be fixed in tissue after placement by use of one or more expanding fixation elements. An expanding fixation element is provided on an implantable lead and configured to secure one or both of a subcutaneous electrode and the lead body within subcutaneous non-intrathoracic tissue. A delivery apparatus comprising a sheath may be included that is configured to introduce the lead to a desired subcutaneous non-intrathoracic location within the patient. A method of lead delivery typically involves introducing a sheath into a subcutaneous non-intrathoracic body location of a patient, providing a lead comprising a lead body and an electrode, and advancing the lead through the sheath and to the subcutaneous non-intrathoracic body location. The method further involves fixing the lead to subcutaneous non-intrathoracic tissue using an expanding fixation element and thereafter removing the sheath from the patient.

RELATED APPLICATIONS

This application claims the benefit of Provisional Patent ApplicationSer. No. 60/462,272, filed on Apr. 11, 2003, to which priority isclaimed pursuant to 35 U.S.C. §119(e) and which is hereby incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates generally to leads for subcutaneouslyimplantable cardiac monitoring and/or stimulation devices, and, moreparticularly, to expandable fixation elements for subcutaneouselectrodes.

BACKGROUND OF THE INVENTION

Implantable cardiac rhythm management systems have been used as aneffective treatment for patients with serious arrhythmias. These systemstypically include one or more leads and circuitry to sense signals fromone or more interior and/or exterior surfaces of the heart. Such systemsalso include circuitry for generating electrical pulses that are appliedto cardiac tissue at one or more interior and/or exterior surfaces ofthe heart. For example, leads extending into the patient's heart areconnected to electrodes that contact the myocardium for monitoring theheart's electrical signals and for delivering pulses to the heart inaccordance with various therapies for treating arrhythmias.

Typical implantable cardioverter/defibrillators (ICDs) include one ormore endocardial leads to which at least one defibrillation electrode isconnected. Such ICDs are capable of delivering high-energy shocks to theheart, interrupting the ventricular tachyarrythmia or ventricularfibrillation, and allowing the heart to resume normal sinus rhythm. ICDsmay also include pacing functionality.

Although ICDs are very effective at preventing Sudden Cardiac Death(SCD), most people at risk of SCD are not provided with implantabledefibrillators. Primary reasons for this unfortunate reality include thelimited number of physicians qualified to perform transvenouslead/electrode implantation, a limited number of surgical facilitiesadequately equipped to accommodate such cardiac procedures, and alimited number of the at-risk patient population that may safely undergothe required endocardial or epicardial lead/electrode implant procedure.For these reasons, subcutaneous ICDs are being developed.

Current ICDs utilize subcutaneous electrodes that may be prone tomigrate in the subcutaneous tissue layer due to, for example, gravity,patient mobility, or patient interaction (e.g., twiddler's syndrome).Such migration may be detrimental to the performance of a subcutaneouselectrode system because monitoring, detection, and defibrillationefficacy is typically very sensitive to electrode position/orientation.

Existing subcutaneous leads have typically relied on redundancy toaddress the problem of subcutaneous electrode migration. For example, asubcutaneous array may include three long coil electrodes, even thoughall three coils are not necessary when properly placed. Becausemigration may occur, the three long fingers provide adequate coverage tomaintain defibrillation efficacy.

There is a need for more precise electrode placement that solves theproblem of subcutaneous electrode migration. There is a further need fora fixation approach for subcutaneous leads that provides for improvedsubcutaneous system performance, such as by providing more consistentdefibrillation and/or pacing thresholds and potentially lowering suchthresholds. The present invention fulfills these and other needs, andaddresses deficiencies in known systems and techniques.

SUMMARY OF THE INVENTION

The present invention is directed to subcutaneous systems and leadsthat, in general, can be fixed in tissue after placement. Embodiments ofthe present invention are directed to subcutaneous leads thatincorporate one or more expanding fixation elements. Further embodimentsof the present invention are directed to methods of placement andmethods of fixation of subcutaneously implantable leads.

An implantable lead in accordance with an embodiment of the presentinvention is directed to a lead body with a supported electrode. Theelectrode is configured for subcutaneous non-intrathoracic placementwithin a patient. An expanding fixation element is provided on theimplantable lead and configured to secure one or both of thesubcutaneous electrode and the lead body in subcutaneousnon-intrathoracic tissue. A delivery apparatus comprising a sheath maybe included that is configured to introduce the lead to a desiredsubcutaneous non-intrathoracic location within the patient.

Another embodiment of the present invention is directed to a method oflead delivery involving introducing a sheath into a subcutaneousnon-intrathoracic body location of a patient, providing a leadcomprising a lead body and an electrode, and advancing the lead throughthe sheath and to the subcutaneous non-intrathoracic body location. Themethod further involves fixing the lead to subcutaneousnon-intrathoracic tissue using an expanding fixation element andthereafter removing the sheath from the patient. The method may alsoinvolve longitudinally splitting the sheath when retracting the sheathfrom the patient and enabling an expandable fixation element forengagement with subcutaneous non-intrathoracic tissue.

The above summary of the present invention is not intended to describeeach embodiment or every implementation of the present invention.Advantages and attainments, together with a more complete understandingof the invention, will become apparent and appreciated by referring tothe following detailed description and claims taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are views of a transthoracic cardiac monitoring and/orstimulation device as implanted in a patient;

FIG. 2 illustrates a lead in accordance with the present invention,inserted in a dissected subcutaneous path leading from the can;

FIG. 3A is a plan view of a lead enclosed within a sheath prior todeployment of fixation elements in accordance with the presentinvention;

FIGS. 3B and 3C are plan views of a lead having an expanding regionbefore (FIG. 3B) and after (FIG. 3C) expansion in accordance with thepresent invention;

FIG. 4 is a magnified view of one embodiment of a lead having anelectrode, the lead implemented to include fixation arrangements inaccordance with the present invention;

FIG. 5 is a magnified view of another embodiment of a lead having anelectrode, the lead implemented to include fixation arrangements inaccordance with the present invention;

FIG. 6 is a magnified view of a further embodiment of a lead having anelectrode, the lead implemented to include fixation arrangements inaccordance with the present invention;

FIG. 7 is a magnified view of yet another embodiment of a lead having anelectrode, the lead implemented to include fixation arrangements inaccordance with the present invention;

FIG. 8A is a magnified view of a further embodiment of a lead having anelectrode, the lead implemented to include fixation arrangements inaccordance with the present invention;

FIG. 8B is an end view of the embodiment illustrated in FIG. 8A;

FIG. 9A is a magnified view of another embodiment of a lead having anelectrode, the lead implemented to include a fixation arrangement inaccordance with the present invention;

FIG. 9B is an end view of the embodiment illustrated in FIG. 9A;

FIG. 9C is a magnified view of another embodiment of a lead having anelectrode, the lead implemented to include a fixation arrangement inaccordance with the present invention;

FIG. 9D is an end view of the embodiment illustrated in FIG. 9C;

FIG. 9E is a magnified view of another embodiment of a lead having anelectrode, the lead implemented to include a fixation arrangement inaccordance with the present invention;

FIG. 9F is an end view of the embodiment illustrated in FIG. 9E;

FIG. 9G is a magnified sectional view of another embodiment of a leadimplemented to include a fixation arrangement in accordance with thepresent invention;

FIGS. 10A, 10B, 10C and. 10D are sectional views of various times inaccordance with the present invention;

FIG. 11 illustrates a lead in accordance with the present invention,inserted in a dissected subcutaneous path leading from the can, where anoffset helical electrode/fixation element is illustrated fixed to thetissue;

FIG. 12 is a plan view of a lead enclosed within a sheath prior todeployment of a fixation element in accordance with the presentinvention;

FIG. 13 is a magnified view of one embodiment of a lead having anelectrode, the lead implemented to include a fixation arrangement inaccordance with the present invention;

FIG. 14 is a magnified end view of the embodiment of FIG. 13;

FIG. 15 is a magnified view of a further embodiment of a lead having anelectrode, the lead implemented to include a fixation arrangement inaccordance with the present invention; and

FIG. 16 is a magnified end view of the embodiment of FIG. 15.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail below. It is to be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the invention isintended to cover all modifications, equivalents, and alternativesfalling within the scope of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

In the following description of the illustrated embodiments, referencesare made to the accompanying drawings, which form a part hereof, and inwhich is shown by way of illustration various embodiments in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized, and structural and functional changes maybe made without departing from the scope of the present invention.

A device employing an implantable lead implemented in accordance withthe present invention may incorporate one or more of the features,structures, methods, or combinations thereof described herein below. Forexample, a subcutaneous cardiac monitor or stimulator may be implementedto include one or more of the features and/or processes described below.It is intended that such a device or method need not include all of thefeatures and functions described herein, but may be implemented toinclude selected features and functions that, in combination, providefor unique structures and/or functionality.

In general terms, an implantable lead implemented in accordance with thepresent invention may be used with a subcutaneous cardiac monitoringand/or stimulation device. One such device is an implantabletransthoracic cardiac monitoring and/or stimulation (ITCS) device thatmay be implanted under the skin in the chest region of a patient. TheITCS device may, for example, be implanted subcutaneously such that allor selected elements of the device are positioned on the patient'sfront, back, side, or other body locations suitable for monitoringcardiac activity and delivering cardiac stimulation therapy. It isunderstood that elements of the ITCS device may be located at severaldifferent body locations, such as in the chest, abdominal, or subclavianregion with electrode elements respectively positioned at differentregions near, around, in, or on the heart.

The primary housing (e.g., the active or non-active can) of the ITCSdevice, for example, may be configured for positioning outside of therib cage at an intercostal or subcostal location, within the abdomen, orin the upper chest region (e.g., subclavian location, such as above thethird rib). In one implementation, one or more electrodes may be locatedon the primary housing and/or at other locations about, but not indirect contact with the heart, great vessel or coronary vasculature.

In another implementation, one or more leads incorporating electrodesmay be located in direct contact with the heart, great vessel orcoronary vasculature, such as via one or more leads implanted by use ofconventional transvenous delivery approaches. In another implementation,for example, one or more subcutaneous electrode subsystems or electrodearrays may be used to sense cardiac activity and deliver cardiacstimulation energy in an ITCS device configuration employing an activecan or a configuration employing a non-active can. Electrodes may besituated at anterior and/or posterior locations relative to the heart.

Referring now to FIGS. 1A and 1B of the drawings, there is shown aconfiguration of an ITCS device implanted in the chest region of apatient at different locations by use of a dissection tool. In theparticular configuration shown in FIGS. 1A and 1B, the ITCS deviceincludes a housing 102 within which various cardiac monitoring,detection, processing, and energy delivery circuitry may be housed. Thehousing 102 is typically configured to include one or more electrodes(e.g., can electrode and/or indifferent electrode). Although the housing102 is typically configured as an active can, it is appreciated that anon-active can configuration may be implemented, in which case at leasttwo electrodes spaced apart from the housing 102 are employed. An ITCSsystem according to this approach is distinct from conventionalapproaches in that it is preferably configured to include a combinationof two or more electrode subsystems that are implanted subcutaneously.

In the configuration shown in FIGS. 1A and 1B, a subcutaneous electrode104 may be positioned under the skin in the chest region and situateddistal from the housing 102. The subcutaneous and, if applicable,housing electrode(s) may be positioned about the heart at variouslocations and orientations, such as at various anterior and/or posteriorlocations relative to the heart. The subcutaneous electrode 104 iselectrically coupled to circuitry within the housing 102 via a leadassembly 106. One or more conductors (e.g., coils or cables) areprovided within the lead assembly 106 and electrically couple thesubcutaneous electrode 104 with circuitry in the housing 102. One ormore sense, sense/pace or defibrillation electrodes may be situated onthe elongated structure of the electrode support, the housing 102,and/or the distal electrode assembly (shown as subcutaneous electrode104 in the configuration shown in FIGS. 1A and 1B).

In one configuration, the lead assembly 106 is generally flexible. Inanother configuration, the lead assembly 106 is constructed to besomewhat flexible, yet has an elastic, spring, or mechanical memory thatretains a desired configuration after being shaped or manipulated by aclinician. For example, the lead assembly 106 may incorporate agooseneck or braid system that may be distorted under manual force totake on a desired shape. In this manner, the lead assembly 106 may beshape-fit to accommodate the unique anatomical configuration of a givenpatient, and generally retains a customized shape after implantation.Shaping of the lead assembly 106 according to this configuration mayoccur prior to, and during, ITCS device implantation.

In accordance with a further configuration, the lead assembly 106includes a rigid electrode support assembly, such as a rigid elongatedstructure that positionally stabilizes the subcutaneous electrode 104with respect to the housing 102. In this configuration, the rigidity ofthe elongated structure maintains a desired spacing between thesubcutaneous electrode 104 and the housing 102, and a desiredorientation of the subcutaneous electrode 104/housing 102 relative tothe patient's heart. The elongated structure may be formed from astructural plastic, composite or metallic material, and includes, or iscovered by, a biocompatible material. Appropriate electrical isolationbetween the housing 102 and the subcutaneous electrode 104 is providedin cases where the elongated structure is formed from an electricallyconductive material, such as metal.

In one configuration, the rigid electrode support assembly and thehousing 102 define a unitary structure (i.e., a single housing/unit).The electronic components and electrode conductors/connectors aredisposed within or on the unitary ITCS device housing/electrode supportassembly. At least two electrodes are supported on the unitary structurenear opposing ends of the housing/electrode support assembly. Theunitary structure may have, for example, an arcuate or angled shape.

According to another configuration, the rigid electrode support assemblydefines a physically separable unit relative to the housing 102. Therigid electrode support assembly includes mechanical and electricalcouplings that facilitate mating engagement with correspondingmechanical and electrical couplings of the housing 102. For example, aheader block arrangement may be configured to include both electricaland mechanical couplings that provide for mechanical and electricalconnections between the rigid electrode support assembly and housing102. The header block arrangement may be provided on the housing 102 orthe rigid electrode support assembly or both. Alternatively, amechanical/electrical coupler may be used to establish mechanical andelectrical connections between the rigid electrode support assembly andthe housing 102. In such a configuration, a variety of differentelectrode support assemblies of varying shapes, sizes, and electrodeconfigurations may be made available for physically and electricallyconnecting to a standard ITCS device.

It is noted that the electrodes and the lead assembly 106 may beconfigured to assume a variety of shapes. For example, the lead assembly106 may have a wedge, chevron, flattened oval, or a ribbon shape, andthe subcutaneous electrode 104 may include a number of spacedelectrodes, such as an array or band of electrodes. Moreover, two ormore subcutaneous electrodes 104 may be mounted to multiple electrodesupport assemblies 106 to achieve a desired spaced relationship amongstthe subcutaneous electrodes 104. Accordingly, subcutaneous leads of thepresent invention may be shaped appropriately for specific electrodes orfamilies of electrodes and electrode support assemblies.

The ITCS device may be used within the structure of an advanced patientmanagement (APM) system. Advanced patient management systems may allowphysicians to remotely and automatically monitor cardiac and respiratoryfunctions, as well as other patient conditions. In one example,implantable cardiac rhythm management systems, such as cardiacpacemakers, defibrillators, and resynchronization devices, may beequipped with various telecommunications and information technologiesthat enable real-time data collection, diagnosis, and treatment of thepatient. Various embodiments described herein may be used in connectionwith advanced patient management. Methods, structures, and/or techniquesdescribed herein, which may be adapted to provide for remotepatient/device monitoring, diagnosis, therapy, or other APM relatedmethodologies, can incorporate features of one or more of the followingreferences: U.S. Pat. Nos. 6,221,011; 6,270,457; 6,277,072; 6,280,380;6,312,378; 6,336,903; 6,358,203; 6,368,284; 6,398,728; and 6,440,066,which are hereby incorporated herein by reference.

Referring now to FIG. 2, an ITCS system 200 is illustrated whichincludes a can 250 with a lead 241 inserted into a subcutaneousdissection path 220. The lead 241 includes an electrode 230 and a leadbody 240. The electrode 230 is here illustrated at the distal end of thelead body 240. The subcutaneous dissection path 220 lies withinsubcutaneous tissue of a patient as illustrated in FIGS. 1A and 1B. Thelead 241 may be inserted into the subcutaneous dissection path 220 byitself, or may also be inserted with use of a sheath 320 as illustratedin FIG. 3A.

In FIG. 3A, a proximal end of the lead body 240 extends from the sheath320, with the electrode 230 enclosed within the lumen of the sheath 320.The electrode 230 is illustrated that includes fixation elements 232 and234 respectively provided at distal and proximal ends of the electrode230. It should be understood that any number of such fixation elementsmay be employed to fix the electrode 230 within subcutaneous tissue.

The fixation elements 232 and 234 may include, for example, anexpandable fixation mechanism, such as a spongy material that ispreferably, but not necessarily, compressed within the lumen of thesheath 320 during delivery. According to one delivery approach, the lead241 may be inserted into the dissection path, such as dissection path220 shown in FIG. 2, while inside the sheath 320. After positioning thesheath 320 at the desired location within subcutaneous tissue, thesheath 320 may be retracted or otherwise separated from the lead 241.Retracting the sheath 320 from the electrode 230 and the lead body 240permits the fixation elements 232 and 234 to expand and affix theelectrode 230 within the subcutaneous tissue.

A suitable material for constructing the fixation elements 232 and 234is scleral sponge. However, the fixation elements 232 and 234 may beconstructed from any implantable material capable of expansion.Expansion of the fixation elements 232 and 234 may occur due to theirrelease from the sheath 320, from uptake of body fluid, from an injectedmaterial, or other means of expansion. For example, a fluid may beinjected into an expandable balloon fixation element with a one-wayvalve or stopper.

Other embodiments of expanding fixation elements are illustrated inFIGS. 3B and 3C. In FIG. 3B, an expanding collar 330 and an expandinglead portion 340 are illustrated in their respective pre-expansionconfigurations. The expanding collar 330 and lead portion 340 may, forexample, be components made of a mixture of a biocompatible polymer anda water-soluble additive. By way of illustration, silicone rubber and awater-soluble additive such as glycerol represent one combination ofmaterials useful for producing the expanding collar 330 and theexpanding lead portion 340.

For example, the expanding collar 330 and/or lead portion 340 mayinclude more than one additive and/or concentrations of one or moreadditives. At a first additive concentration, by way of illustration,the expanding collar 330 and/or lead portion 340 may expand for acutefixation, and remain expanded for continued chronic fixation. At asecond additive concentration, by way of further illustration, theexpanding collar 330 and/or lead portion 340 may expand for acutefixation, and the additive may then subsequently dissolve to providepores that promote chronic tissue ingrowth. Similarly, a first additivemay provide expansion and a second additive may provide porosity afterthe second additive is dissolved.

The expanded tip or collar 330 may itself provide a press-fit in thesurrounding subcutaneous tissue, ensuring fixation, or may also provideporosity for promoting tissue ingrowth. By using other compositions, theadditive(s) within the material may create pockets that combine withinthe component sufficiently to create pores that communicate with thecomponent surface, which promotes tissue ingrowth. An example ofadditives that require a containment matrix or scaffolding for supportinclude, but are not limited to, water soluble materials such asglycerol, mannitol, sodium chloride, and potassium chloride, as well aswater soluble pharmaceutical agents such as, for example, dexamethasonesodium phosphate.

In another example involving use of expanding material compositions, anexpanding polymer may be used alone or in combination with non-expandingpolymers or other expanding materials. For example, a hydrogel may beused as an expanding polymeric additive to a non-expanding silicone, orin combination with an expanding material such as glycerol as isdescribed above. A non-exhaustive, non limiting list of hydrogels usefulin accordance with the present invention includes methyl methacrylate,poly(2-hydroxyethel methacrylate) gel, methacrylic acid, and otherpolyacid gels and methacrylate hydrogels.

Provision of an expanding polymer within or on an implantable lead bodyor lead component may provide for one or more of acute expandingfixation only, acute and chronic expanding fixation, and acute expandingfixation with dissolution of a non-polymeric additive for promotingtissue ingrowth and subsequent chronic fixation. A non-exhaustivenon-limiting listing of expandable polymers useful in accordance withthe present invention includes: vinylpyrrolidone, silicone rubber,polyurethane, polyacrylamide, and polyvinylpyrrolidone.

Polymeric expansion can be achieved in at least three ways. By way of afirst example, a polymer may absorb environmental water in one of twofashions. Polymers that expand according to the first fashion arecompounded with one or more of the additives listed above. The isolatedadditive inclusions will dissolve as water penetrates the polymer. Sincethe concentration of water in the isolated additive inclusion site wouldbe less than that of the outer environment, water would naturallycontinue to enter the inclusion site, thereby bringing about expansion.This process would terminate once the growing internal “bubble” ofadditive solution encountered sufficient internal polymeric forces. Inthe event that the strength of the polymer was insufficient to generatethose counteracting forces, the bubble would continue to grow until thebubble burst and the additive solution was released to the environment.This process would take place with any of the polymers listed.

Polymers that expand according to the second fashion absorbenvironmental water, and are usually provided initially in a dry state.Water or fluid absorption causes the polymeric component to expand. Thisis one mechanism for the hydrogel polymers list above. In the case ofosmotic swelling utilizing an expanding polymer the absorbed watersupplied by the body's aqueous environment penetrates the polymer toprovide component expansion. The subsequent reaction forces generatedwithin the material eventually balance the osmotic forces so thatdestructive expansion does not occur.

A second way expansion can be achieved uses a polymer that is exposed tochanges in environmental pH. This is the case for some of the hydrogelformulations listed above. For example, a polymer such as thepoly(2-hydroxyethel methacrylate) gel described above exhibitspolymorphism of the polymer chain structure as pH changes. In a firststate, the polymer may have a first structure that undergoes a changewhen it is immersed into the body's aqueous environment. Theenvironmental pH will cause the polymer to change to a second structure,and bring about an expansion of the material. Further, the pH-sensitivepolymers may also experience still further expansion when formulatedwith one or more additives listed above.

A third way expansion can be achieved uses a polymer that is exposed toan environment containing mobile substances, other than water, thatwould leave that environment to enter or partition into the polymer. Awell-known example of this type of expansion is the uptake of lipid-likesubstances from the blood by early silicone rubber formulations such asmaterials used to manufacture early artificial heart valve poppets. Overtime, after implantation, these silicone rubber poppets “soaked up”enough lipid-like substances to change the shape of the poppet and, insome cases, cause undesired valve failure. Modern formulations ofsilicone rubber are now available that do not exhibit this lipid-uptakebehavior. However, the early formulations of silicone rubber may bebeneficial for applications such as in the present invention. Theabsorption of lipid-like substances into a polymer, such as earlyformulation silicone, would bring about desired expansion to achievefixation. Further, this expansion would be based upon a polymericformulation, and not need the inclusion of additives to providefixation.

In general, expandable polymer materials change shape in response tochanges in their environment. Expanding polymers may be used bythemselves, solely providing expansion, or may be used in combinationwith non-polymeric additives and/or other non-expanding polymers.

FIG. 3C illustrates an expanded collar 350 and an expanded lead portion360. After implantation, collar 330 and lead portion 340 (shown in FIG.3B) expand, and transform into expanded collar 350 and expanded leadportion 360. The expanded collar 350 and portion 360 may be employed incombination and/or by themselves, to fix the lead 241 into tissue.

Turning now to FIG. 4, there is illustrated an embodiment of the lead241 that includes an electrode 230 provided with another fixationarrangement. The lead 241 is shown to include the electrode 230 nowhaving tines 410, 420, 430, 440, 450, and 460 projecting outwardly fromthe body of the electrode 230/lead body 240. Also illustrated are anumber of diagonal grooves 470, 471, 472, 473, and 474.

The tines 410-460 are shown biased away from the lead body 240 by, forexample, manufacturing the times 410-460 using a mechanically elasticmaterial having spring-like qualities such as, for example, metal orplastic. The tines 410-460 may be angled away and proximally oriented,as illustrated in FIG. 4, to allow the lead 241 to be easily insertedinto the dissection path in a distal direction, but resist being pulledout in a proximal direction. The tines 410-460 provide for both acuteand chronic fixation of the lead 241 into subcutaneous tissue.

After placement and acute fixation of the lead 241 within subcutaneoustissue, the grooves 470-474 provide regions for promoting tissueingrowth, which chronically fixes the lead 241 within the subcutaneoustissue. The grooves 470-474 are denoted by a series of parallel linesoriented diagonally relative to a longitudinal axis of the lead body240. It is contemplated that any number of grooves may be implemented atany angle or at varying angles. For example, a crosshatched pattern ofgrooves 510, as is illustrated in FIG. 5, may be incorporated to promotetissue ingrowth after placement of the lead 241 within subcutaneoustissue. The grooves 470-474 may be of any suitable size, shape, depth orspacing.

As illustrated in FIG. 6, one or more ridges 610 may be used incombination with, or in lieu of, grooves for chronic tissue purchase.The ridges 610 may be configured to provide for chronic fixation of thelead body 240 resulting from tissue ingrowth. Both grooves 510 (FIG. 5)and ridges 610 may also provide a degree of acute fixation, depending onthe size of the grooves 510 or ridges 610. Acutely, the grooves 510 orridges 610 would provide an initial purchase with the tissue. As timeprogresses, the initial immature encapsulation will constrict, resultingin a more firm purchase on the lead 241. As is further illustrated inFIG. 6, a plurality of tines 620, 630, 640, 650, 660, and 670 may beused in combination with other fixation techniques for purposes ofacutely fixing the lead body 240 and/or a lead electrode, as describedearlier. Features such as the plurality of tines 620, 630, 640, 650,660, and 670 may be located on the lead body 240 and/or the electrode230. The tines 620-670 and/or the ridges 610 and/or grooves may be usedin various combinations along with other acute fixation techniques knownin the art, such as, for example, a suture attachment point (not shown)on the lead 241.

Referring now to FIG. 7, another fixation arrangement in accordance withthe present invention is illustrated. According to this embodiment, thefixation arrangement includes one or more textured surfaces or regions710 on the lead body 240 and/or an electrode 230 of the lead 241. Thetextured surface(s) 710 may be employed as a sole chronic fixationmethod or in combination with other chronic fixation arrangements, suchas a set of grooves 720 as is depicted in FIG. 7.

The textured surface 710 promotes tissue ingrowth to provide for chronicfixation of the lead body 240 into subcutaneous tissue. The texturedsurface 710 may be, for example, a porous region of the lead body 240, acoating having surface irregularities, dimples molded into the lead body240 and/or a lead electrode 230, surface treatments from manufacturingprocesses such as sanding or scratching, or other suitable texturing.

Generally at least one acute fixation mechanism is employed incombination with chronic fixation mechanism, to allow sufficient timefor the fixing of the chronic fixation mechanism into the subcutaneoustissue. An appropriate acute fixation mechanism is, for example, asuture placed at the distal end of the lead 241.

According to other fixation arrangements similar to those describedabove, and with reference to FIG. 7, the lead body 240 and/or theelectrode 230 may be configured to incorporate tissue adhesion sitesthat facilitate chronic fixation of the lead body 240 and/or electrode230 in subcutaneous tissue. For example, the adhesion sites may includevoids in the sleeve of the lead body 240 at one or more locations of thesleeve. The adhesion sites may include exposed portions of one or moreelectrodes 230 or other exposed portions of the lead 241 insulation orcovering.

According to another configuration, the adhesion sites may include astructure having a porous surface that promotes subcutaneous tissuein-growth or attachment at the adhesion sites. For example, a metallicannular structure may be disposed at the adhesion site. A metallic ring,for example, having porous surface characteristics may be employed topromote cellular adhesion at the adhesion site. The annular structuremay incorporate the electrode 230 or be separate from the electrode 230.

In accordance with a further configuration, the adhesion sites mayinclude a material that promotes subcutaneous tissue in-growth orattachment at the adhesion sites. For example, the bulk outer sleeve ofthe lead body 240 may be constructed that includes a first polymermaterial that substantially prevents tissue in-growth. Selectiveportions of the lead body 240 may include adhesion sites formed using asecond polymer material that promotes tissue in-growth or attachmentbetween the adhesion sites and subcutaneous tissue contacting theadhesion sites. The second polymer material may, for example, have aporosity, pore sizes or distribution of pore sizes that differ from thatof the first polymer material. By way of further example, the secondpolymer material may differ in terms of hydrophobicity relative to thefirst polymer material.

In one particular configuration, the first polymer material may includea first type of PTFE (polytetrafluoroethylene), and the second polymermaterial of the adhesion sites may include a second type of PTFE. In oneparticular arrangement, the first type of PTFE includes a first type ofePTFE (expanded polytetrafluoroethylene), and the second type of PTFEincludes a second type of ePTFE. The second type of ePTFE preferablydiffers from the first type of ePTFE in terms of one or more ofporosity, pore sizes or distribution of pore sizes. Additional detailsof fixation approaches involving surface texturing, selective materialuse, and other arrangements that facilitate lead/electrode fixation viatissue ingrowth are disclosed in commonly owned U.S. patent applicationSer. No. 10/004,708 (GUID.031 US01) filed Dec. 4, 2001 and entitled“Apparatus and Method for Stabilizing an Implantable Lead,” which ishereby incorporated herein by reference.

Now referring to FIGS. 8A and 8B, details of acute fixation elementsaccording to another embodiment of the present invention are shown. Alead 800 is illustrated that includes a plurality of tines 810, 820,830, 840, 845 (FIG. 8B), 850, 860, 870, 880, and 890 (FIG. 8A). Thetines 810-890 are shown disposed regularly with 90 degreecircumferential placement, and regularly spaced along the length of thelead 800. However, other angles, regularity or irregularity, or numberof tines may be employed in accordance with this embodiment. The tines810-890 are shown, in this illustrative example, to be curved as theyextend from the body of the lead 800. Curvature may assist infacilitating acute fixation by providing ease of movement of the lead800 in a first direction (e.g., axial displacement in a distaldirection), while helping to set the tines into tissue in response tomovement in a second direction (e.g., axial displacement in a proximaldirection). It is contemplated that the tines may be straight, or have acurvature tending away from or toward the body of the lead 800.

Tines configured in accordance with the present invention may also becurved in more than one plane, as is illustrated in FIGS. 9A and 9B. Alead 900 (lead and/or electrode) is shown that includes tines 910, 920,930, 935 (FIG. 9B), 940, 950, and 960 (FIG. 9A). As shown, the tines910-960 are curved upward and away from the lead 900 relative to alongitudinal axis of the lead 900. The tines 910-960 are also curvedaround the circumference of the body of the lead 900 with respect to asecond plane of reference.

The complex curvature illustrated in FIGS. 9A and 9B may be advantageousfor optimally placing and fixing the lead 900 within subcutaneoustissue. This complex curvature provides for ease of inserting andwithdrawing of the lead 900 when the lead 900 is rotated in a firstdirection. If the lead 900 is not rotated, the tines 910-960 set intothe tissue. Further, if the lead 900 is rotated in the counterdirection, the tines 910-960 may be forced into subcutaneous tissue.

Another tine configuration that employs complex curvature is illustratedin FIGS. 9C and 9D for optimally placing and fixing the lead 900 withinsubcutaneous tissue. This complex curvature provides for fixation fromproximal displacement, and from rotation of the lead 900. Tines 921,923, 931, 933, 951, and 953 set into the tissue due to their spring biasoutwardly and upwardly from the lead 900. Placement of this type of leadfixation may be accomplished by direct distal insertion, to compress thetines 921, 923, 931, 933, 951, and 953 during placement and upon releaseof distal motion, the tines 921, 923, 931, 933, 951, and 953 springoutwardly from the lead 900 for fixation.

A further tine configuration that employs complex curvature isillustrated in FIGS. 9E and 9F for optimally placing and fixing the lead900 within subcutaneous tissue. This complex curvature provides forfixation from both proximal and distal displacement, and from rotationof the lead 900. Tines 922, 932, 942, 952, 962, and 972 set into thetissue due to their spring bias outwardly and upwardly from the lead900. Placement of this type of lead fixation may be accomplished byutilization of a sheath, as described earlier, to compress the tines922, 932, 942, 952, 962, and 972 during placement, and upon removal ofthe sheath, the tines 922, 932, 942, 952, 962, and 972 spring outwardlyfrom the lead 900 for fixation.

FIG. 9G is a magnified sectional view of another embodiment of a leadimplemented to include a fixation arrangement in accordance with thepresent invention. Tines 973 and 974 set into the tissue due to theirspring bias outwardly and upwardly from the lead 900. Placement of thistype of lead fixation may be accomplished by utilization of a sheath, asdescribed earlier, to compress the tines 973 and 974 during placement,and upon removal of the sheath, the tines 973 and 974 spring outwardlyfrom the lead 900 for fixation.

FIGS. 10A,10B, 10C and 10D illustrate various shapes for tines inaccordance with the present invention. In FIG. 10A, a tine 1010 is shownprojecting from the lead 900. The tine 1010 has a single tip 1080. Thetine 1010 is shaped to spring away from the lead 900 body.

For descriptive ease, consider a lead in the plane of FIGS. 10A, 10B,10C and 10D, with the lead 900 moving from left to right in the plane ofthe figures. If the lead 900 were inserted, in this drawing from theleft to the right, the tine 1010 would tend to collapse into the lead900 and allow forward progress of the lead 900. If the lead 900 were tobe pulled from right to left in FIG. 10A, the tine 1010 would tend toset into tissue by the single tip 1080.

Similarly to the tine of FIG. 10A, a tine 1020 of FIG. 10B would alsoflex and set under the same movement. However, the tine 1020, not assubstantial as the tine 1010 of FIG. 10A, would more easily collapse andcompress under left to right motion, and may provide less resistance toright to left motion.

Referring now to FIG. 10C, a tine 1030 is illustrated with a first point1050 and a second point 1040. The shape of the tine 1030, along with thesecond point 1040, creates a barb 1060. The barb 1060, similar to afishhook barb, provides for not only resistance to right to left motion,but also for resistance to further left to right motion after being set.This arrangement provides for ease of insertion in a left to rightdirection, a resistance to right to left movement, and subsequently alsoprovides resistance to further left to right movement after being set.

Referring to FIG. 10D, a straight tine 1012 is illustratedperpendicularly projecting from the lead 900 body. The straight tine1012 may be compressed and/or spring biased in the lumen of a sheath(such as, for example, the sheath 320 in FIG. 3A) during delivery of thelead 900, such that the straight tine 1012 sets into tissue when thesheath is removed. In another embodiment, the rigidity of the straighttine 1012 may be designed such that a set level of resistance isprovided by the straight tine 1012 when it is moved within tissue. Byadjusting the rigidity, the level of fixation of the lead 900, and theassociated ease of insertion/relocation, may be predetermined by design.Rigidity may be altered by material selection, geometry, of other meansknown in the art.

Referring now to FIG. 11, an ITCS system 200 is illustrated whichincludes a can 250 with a lead 241 inserted into a dissection path 220.The lead 241 includes an electrode 230, here illustrated at the distalend of the lead body 240. The subcutaneous dissection path 220 lieswithin subcutaneous tissue of a patient as illustrated in FIGS. 1A and1B. An offset helix 260 is employed as a fixation element useable to fixthe lead 241 into tissue in accordance with the present invention.Typically, the helix 260 is configured to define all or at least part ofthe electrode 230.

FIG. 12 illustrates the lead 241 inserted into the tear-away sheath 320as described with an earlier embodiment. After placing the lead 241 insubcutaneous tissue, the sheath 320 is retracted from the subcutaneoustunnel, typically in a peel-away fashion. The lead 241 may be fixed intothe tissue by rotating the lead 241 as will be described in furtherdetail below.

FIGS. 13 and 14 show a plan view and end view respectively of anembodiment of the present invention. In FIG. 13, a helical coil 260 maybe used as a fixation element to fix the lead body 240 into tissue whenthe electrode 230 is positioned in a desired location. The helical coil260 is attached to the distal end of the lead body 240 at attachmentpoint 262. Rotation of the lead body 240 causes rotation of the helicalcoil 260, thereby rotating sharp end 400.

Although helical coil 260 is illustrated having uniform pitch,cylindrical cross-section, constant thickness of coil, it iscontemplated that any helical or screw-like structure may be used inaccordance with the present invention. The helix may be of non-uniformand/or tapering cross-section; the pitch may be non-uniform; and theshape and thickness of the coil may be varied without departing from thescope of the present invention.

As the lead 241 is rotated, the sharp end 400 contacts the wall of thedissected tissue path and penetrates into subcutaneous tissue. As thelead 241 is further rotated, the sharp end 400 burrows through thetissue, repeatedly penetrating the wall and progressing forward as thewinding of the helical coil 260 dictates. This effectively screws thehelical coil 260 into the wall of the tissue, thus fixing the lead 241.

In another embodiment, the helical coil 260 may be rotatableindependently of the lead 241. As the helical coil 260 is rotated orformed via extension, the sharp end 400 contacts the wall of thedissected tissue path and penetrates into subcutaneous tissue. As thehelical coil is further rotated or further extended, the sharp end 400burrows through the tissue, repeatedly penetrating the wall andprogressing forward as the winding of the helical coil 260 dictates.This effectively screws the helical coil 260 into the wall of thetissue, thus fixing the lead 241.

In the embodiment illustrated in FIGS. 13 and 14, the helical coil 260is seen to be larger in diameter than the lead body 240. An advantage ofemploying the helical coil 260 that is larger than the lead body 240 isthe assurance that as the lead lies within the dissected tissue tunnel,the sharp end 400 penetrates the tunnel wall and provide fixation whenrotated. If the helical coil 260 were the same size or smaller than thelead body 240 diameter, the lead body may prevent the sharp end 400 frominitiating penetration unless the lead body 240 is pushed distally alongthe dissection tunnel until penetration occurs. This pushing of the leadmay cause the electrode 230 to be moved distally from an optimumfixation location.

Referring now to FIGS. 15 and 16, a plan view and end view respectivelyof another embodiment of the present invention is illustrated. In FIG.15, an offset helical coil 661 may be used as a fixation element to fixthe lead body 240 into tissue when the electrode 230 is positioned in adesired location. The offset helical coil 661 is attached to the distalend of the lead body 240 at attachment point 662. Rotation of the leadbody 240 causes rotation of the offset helical coil 661, rotating sharpend 600.

As the lead body 240 is rotated, the sharp end 600 contacts the wall ofthe dissected tissue path and penetrates into subcutaneous tissue. Asthe lead body 240 is further rotated, the sharp end 600 burrows throughthe tissue, repeatedly penetrating the wall and progressing forward asthe winding of the offset helical coil 661 dictates. This effectivelyscrews the offset helical coil 661 into the wall of the tissue, thusfixing the lead 241.

In the embodiment illustrated in FIGS. 15 and 16, as best seen in FIG.16, the offset helical coil 661 is seen to have an offset central axisrelative to the longitudinal axis of the lead body 240. An advantage ofemploying the offset helical coil 661 offset from the lead body 240 isthe assurance that as the lead lies within the dissected tissue tunnel,the sharp end 600 penetrates the tunnel wall and provides fixation whenrotated.

Coils 260 and 661 may be manufactured using a spring material such as,for example, metal, such that coils 260 and 661 deform within the sheath320 when being advanced to their fixation locations. Upon removal of thesheath 320, coils 260 and 661 spring into their larger or offsetconfigurations to affect fixation into tissue. Coils 260 and 661 mayalso be manufactured using a shape memory alloy such as, for example,Nitinol, such that coils 260 and 661 have a first, non-penetratingshape, when being advanced through the dissection path. Upon beingsubjected to body temperature or artificially heated, coils 260 and 661return to a shape such as described above to affect fixation.

It should be understood that any number, type, or combination offixation elements have been contemplated, and that the number, types,and combinations presented above are by way of example only. Variousmodifications and additions can be made to the preferred embodimentsdiscussed hereinabove without departing from the scope of the presentinvention. Accordingly, the scope of the present invention should not belimited by the particular embodiments described above, but should bedefined only by the claims set forth below and equivalents thereof.

1. An implantable lead configured for placement within a tunnel formedin subcutaneous non-intrathoracic tissue, comprising: a lead body; acardiac electrode supported by the lead body, the cardiac electrodeconfigured for one or both of sensing cardiac activity and deliveringcardiac stimulation energy from a location within the tunnel; and anexpandable fixation element provided on the implantable lead andcomprising a material that undergoes a volumetric change when placed insubcutaneous non-intrathoracic tissue, the expandable fixation elementconfigured to expand by body fluid absorption and to chronically secureone or both of the cardiac electrode and the lead body withinsubcutaneous non-intrathoracic tissue defining the tunnel by tissuein-growth into pores of the expandable fixation element.
 2. The leadaccording to claim 1, wherein the expandable fixation element isprovided on the cardiac electrode.
 3. The lead according to claim 1,wherein the expandable fixation element comprises a sponge.
 4. The leadaccording to claim 1, wherein the expandable fixation element comprisesa scleral sponge.
 5. The lead according to claim 1, wherein theexpandable fixation element comprises a plurality of sponges arranged ina spaced relationship.
 6. The lead according to claim 1, wherein theexpandable fixation element comprises an expandable portion of the leadbody.
 7. The lead according to claim 6, wherein the expandable portionof the lead body comprises an additive in a polymer.
 8. The leadaccording to claim 7, wherein the additive comprises glycerol.
 9. Thelead according to claim 6, wherein the expandable portion of the leadbody comprises an expandable polymer.
 10. The lead according to claim 9,wherein the expandable polymer comprises hydrogel.
 11. The leadaccording to claim 1, wherein the expandable fixation element comprisesan expandable collar coupled to the lead body.
 12. The lead according toclaim 11, wherein the expandable collar comprises an additive in apolymer.
 13. The lead according to claim 12, wherein the additivecomprises glycerol.
 14. An implantable lead system configured forplacement within a tunnel formed in subcutaneous non-intrathoracictissue, comprising: a lead comprising a lead body and a cardiacelectrode, the lead configured for placement within the tunnel, thecardiac electrode configured for one or both of sensing cardiac activityand delivering cardiac stimulation energy from a location within thetunnel; an expandable fixation element provided on the lead andcomprising a material that undergoes a volumetric change when placed insubcutaneous non-intrathoracic tissue, the expandable fixation elementconfigured to expand by body fluid absorption and to chronically secureone or both of the cardiac electrode and the lead body withinsubcutaneous non-intrathoracic tissue defining the tunnel by tissuein-growth into pores of the expandable fixation element; and a deliveryapparatus configured to introduce the lead to a desired subcutaneousnon-intrathoracic location within the tunnel.
 15. The lead systemaccording to claim 14, wherein the expandable fixation element comprisesone or more sponges.
 16. The lead system according to claim 14, whereinthe expandable fixation element comprises one or more scleral sponges.17. The lead system according to claim 14, wherein a lumen of thedelivery apparatus is dimensioned to compress the expandable fixationelement while permitting axial displacement of the lead within thelumen.
 18. The lead system according to claim 14, wherein the deliveryapparatus comprises a sheath having a longitudinal pre-stress linearrangement to facilitate sheath separation during retraction of thesheath from the patient.
 19. The lead system according to claim 14,wherein the expandable fixation element is provided on the cardiacelectrode.
 20. The lead system according to claim 14, wherein theexpandable fixation element comprises a plurality of sponges arranged ina spaced relationship.
 21. The lead system according to claim 14,wherein the expandable fixation element comprises an expandable portionof the lead body.
 22. The lead system according to claim 21, wherein theexpandable portion of the lead body comprises an additive in a polymer.23. The lead system according to claim 22, wherein the additivecomprises glycerol.
 24. The lead according to claim 21, wherein theexpandable portion of the lead body comprises an expandable polymer. 25.The lead system according to claim 24, wherein the expandable polymercomprises a hydrogel.
 26. The lead system according to claim 14, whereinthe expandable fixation element comprises an expandable collar coupledto the lead body.
 27. The lead system according to claim 26, wherein theexpandable collar comprises an additive in a polymer.
 28. The leadsystem according to claim 27, wherein the additive comprises glycerol.29. The lead according to claim 26, wherein the expandable collarcomprises an expandable polymer.
 30. The lead system according to claim29, wherein the expandable polymer comprises a hydrogel.
 31. A method oflead stabilization, comprising: creating a tunnel in subcutaneousnon-intrathoracic tissue of a patient; providing a lead comprising alead body, a cardiac electrode, and an expandable fixation elementcomprising a material that undergoes a volumetric change when placed insubcutaneous non-intrathoracic tissue, the cardiac electrode configuredfor one or both of sensing cardiac activity and delivering cardiacstimulation energy from a location within the tunnel; advancing the leadinto the tunnel; and volumetrically expandably securing one or both ofthe lead body and the cardiac electrode within subcutaneousnon-intrathoracic tissue defining the tunnel at a fixation site usingthe expandable fixation element.
 32. The method according to claim 31,wherein the expandable fixation element expands to an effective diameterlarger than the diameter of the lead body to engage the subcutaneousnon-intrathoracic tissue at the fixation site.
 33. The method accordingto claim 31, wherein the expandable fixation element comprises one ormore expandable fixation elements that expand to fixedly engage thesubcutaneous non-intrathoracic tissue at one or more fixation sites. 34.The method according to claim 31, further comprising modifying theposition or orientation of the expandable fixation element when the leadis advanced within the lumen.
 35. The method according to claim 34,wherein modifying the position or orientation comprises resilientlydisplacing the expandable fixation element when the lead is advancedwithin the lumen.
 36. A method of lead delivery, comprising: creating atunnel in subcutaneous non-intrathoracic tissue of a patient;introducing a sheath into the tunnel; providing a lead comprising a leadbody and a cardiac electrode configured for one or both of sensingcardiac activity and delivering cardiac stimulation energy from alocation within the tunnel, the lead comprising an expandable fixationelement that undergoes a volumetric change when placed in subcutaneousnon-intrathoracic tissue; advancing the lead through the sheath and intothe tunnel; volumetrically expandably fixing the lead withinsubcutaneous non-intrathoracic tissue defining the tunnel by tissuein-growth into pores of the expandable fixation element; and removingthe sheath from the patient.
 37. The method according to claim 36,wherein removing the sheath comprises longitudinally splitting thesheath when removing the sheath from the patient.
 38. The methodaccording to claim 36, wherein removing the sheath comprises enablingthe fixation element for expandably fixing the lead within thesubcutaneous non-intrathoracic tissue.
 39. The method according to claim36, wherein advancing the lead through the sheath comprises modifying aposition or an orientation of the expandable fixation element providedon one or both of the lead body and cardiac electrode.
 40. The methodaccording to claim 36, wherein advancing the lead through the sheathcomprises compressing the expandable fixation element provided on one orboth of the lead body and cardiac electrode.
 41. The method according toclaim 36, wherein fixing the lead comprises expanding a portion of thelead to fix one or both of the lead body and the electrode within thesubcutaneous non-intrathoracic tissue.
 42. An implantable leadconfigured for placement within a tunnel formed in subcutaneousnon-intrathoracic tissue, comprising: a lead body; a cardiac electrodesupported by the lead body, the cardiac electrode configured for one orboth of sensing cardiac activity and delivering cardiac stimulationenergy from a location within the tunnel; and a volumetricallyexpandable portion provided on the implantable lead, the expandableportion configured to expand by bodily fluid absorption and to providepores that promote tissue in-growth for chronic fixation to subcutaneousnon-intrathoracic tissue defining the tunnel.
 43. The lead according toclaim 42, wherein the expandable portion comprises an additive in apolymer.
 44. The lead system according to claim 43, wherein the additivecomprises glycerol.
 45. The lead according to claim 42, wherein theexpandable portion comprises an expandable polymer.
 46. The lead systemaccording to claim 45, wherein the expandable polymer comprises ahydrogel.
 47. The lead system according to claim 42, wherein theexpandable portion comprises one or more sponges.
 48. The lead systemaccording to claim 42, wherein the expandable portion comprises one ormore scleral sponges.
 49. The lead system according to claim 42, whereinthe expandable portion comprises an expandable collar coupled to theimplantable lead.
 50. The lead according to claim 42, wherein theexpandable portion comprises first and second additives, the firstadditive configured to provide expansion and the second additiveconfigured to provide the pores.
 51. The lead according to claim 42,wherein the expandable portion comprises a polymer having first andsecond additive concentrations, the first additive concentrationconfigured to provide expansion and the second additive concentrationconfigured to provide the pores.